In the 1930's, his novels I, Claudius (1934) and Claudius the God (1935) went through many printings and finally provided Graves and his family with some financial stability.

In his author's notes to I,Claudius he refers to Tacitus, Suetonius and Dio and Claudius' speech on the Aeduans and his letter to the Alexandrians.

In his author's notes to Claudius the God, Graves writes: 'Some reviewers of I,Claudius, the prefatory volume to Claudius the God, suggested that in writing it I had merely consulted Tacitus' Annals and Suetonius' Twelve Caesars, run them together, and expanded the result with my own "vigorous fancy." This was not so; nor is it the case here. Among the Classical writers who have been borrowed from in the composition of Claudius the God are Tacitus, Dio Cassius, Suetonius, Pliny, Varro, Valerius Maximus, Orosius, Frontinus, Strabo, Caesar, Columella, Plutarch, Josephus, Diodorus Siculus, Photius, Xiphilinus, Zonaras, Seneca, Petronius, Juvenal, Philo, Celsus, the authors of the Acts of the Apostles and of the pseudo-gospels of Nicodemus and St. James and Claudius himself in his surviving letters and speeches. Few incidents here given are wholly unsupported by historical authority of some sort or other and I hope none are historically incredible. No character is invented.' a little defensive?